With https://gerrit.wikimedia.org/r/#/c/200525/, the class role::package::builder::labs was removed. However, its documentation is still up at https://doc.wikimedia.org/puppet/classes/__site__/role/package/builder/labs.html which is linked for example when you have added role::package::builder::labs to your project-specific Puppet groups on wikitech.
Most of the publish jobs use rsync and delete any extra files. However this one is still running on gallium directly and presumably Puppet's built-in doc generator does not clean up foreign files in the output directory:
- shell: | /usr/bin/puppet doc \ --mode rdoc \ --outputdir /srv/org/wikimedia/doc/puppet \
See T86659. This is fixed when it moves to labs and publishes via rsync.